1. Field of the Invention
The present invention relates to a display, and more particularly, to a circuit which is used to generate horizontal synchronizing signal of a display and associated method.
2. Description of the Prior Art
In a display, when received image is transferred by Component Video Connector (i.e. Y/Pb/Pr interface), the luminance signal(Y) needs to generate horizontal synchronizing signal additionally for the following use.
Refer to FIG. 1, which is a diagram illustrating the luminance signal Y and the wanted horizontal synchronizing signal Hsync. The luminance signal Y includes the horizontal synchronizing pulse, front porch, back porch, and the active video data of the Nth line on the screen. A display uses a comparator to determine whether the luminance signal Y is smaller than a reference voltage or not to decide if it is receiving the horizontal synchronizing pulse. Then according to the result, it generates the horizontal synchronizing signal Hsync.
However, refer to FIG. 2, which is a waveform diagram illustrating the horizontal synchronizing pulse of the luminance signal Y. Owing to the luminance signal is unstable in transmission, the maximum voltage Vmax and the minimum voltage Vmin of the horizontal synchronizing pulse are variable. Therefore, the reference voltage Vref which is utilized by comparator to generate the horizontal synchronizing signal Hsync has to vary with the varied maximum voltage Vmax and the varied minimum voltage Vmin of the horizontal synchronizing pulse. In prior art, it uses an analog-to-digital converter to transfer the luminance signal Y into a digital signal. Furthermore, after acquiring the maximum voltage Vmax and the minimum voltage Vmin of the horizontal synchronizing pulse, it decides the reference voltage Vref which is utilized by comparator. However, this conventional approach needs larger chip area and power consumption.